This invention relates to electrical geophysical methods and apparatus for determining the density of porous materials and establishing the porous material geo-electric constants that relate to U.S. Pat. No. 5,861,751.
The objective of the invention is to provide geo-electric density data for construction material that may be used in conjunction with a field method described in U.S. Pat. No. 5,861,751. The combined technique is used for construction quality control and quality assurance (QC/QA), as well as field documentation for submittal to a regulating authority.
Federal, state, and/or local government regulations require a QC/QA program be implemented during the construction phase of building projects that involve compacted fill earthen material. The QC/QA program involves on-site technical or engineering staff that monitor construction activities and prepare certified engineering reports as to the quality of the facility construction compared to the facility design.
In highway construction the in-situ density design specifications are typically dictated by engineering requirements or state/federal regulations. An example of a regulation that calls for a prescriptive compacted fill specification is the Nevada Department of Transportation, Standard Specifications for Road and Bridge Construction, Section 305 Roadbed Modification Subpart 305.03.05. These regulations contain minimum design criteria for the construction of a highway roadbed. The regulation states:
xe2x80x9cAfter the materials have been satisfactorily mixed, the mixture shall be bladed and compacted to a ninety-five (95) percent relative maximum density as determined by Test Method No. Nev. T101. Test Method No. Nev. T102 or T103 may be used to determine the in-place density Test method to be determined by the Engineer.xe2x80x9d
General: Existing Technologies for Measuring Density of a Porous Medium
The state-of-the art methods for measuring density include, but are not limited to, the Standard Test Method for Moisture-Density Relations of Soil-Aggregate Mixtures Using 10-lb (4.54-kg) Rammer and 18-in. (457-mm) Drop, ASTM 1557-78; or, Standard Test Method for Moisture-Density Relations of Soil-Aggregate Mixtures Using 4.4 lb (2.49-kg) Rammer and 12-in (305-mm) Drop, ASTM D698-78; or ASTM D 2922-81; or ASTM D1556. The existing technologies do not use electrical geophysical methods as a part of the operations and calculations.
Related Patents
U.S. Pat. No. 5,861,751 issued Jan. 19, 1999. The title of this patent is: ELECTRICAL GEOPHYSICAL METHODS AND APPARATUS FOR DETERMINING THE IN-SITU DENSITY OF POROUS MATERIAL. D. M. Anderson and W. J. Ehni are co-inventors for the above-mentioned patent.
U.S. Pat. No. 5,861,750 issued Jan. 19, 1999. The title of this patent is: GEOPHYSICAL METHODS AND APPARATUS FOR DETERMINING THE HYDRAULIC CONDUCTIVITY OF POROUS MATERIALS, D. M. Anderson and W. J. Ehni are co-inventors for the above-mentioned patent. The apparatus and method of acquiring the electrical resistivity field data for determining relative in-situ density of porous material uses portions of the prior art.
Applicable Background Art
Development of an electrical geophysical method and apparatus for determining the in-situ density of porous materials at the earth""s surface utilizes two primary principles of applied geophysics. Both of the geophysical principals had their origin in the petroleum industry and were not considered, assessed, examined, or adapted for use for geotechnical engineering until Anderson and Ehni recognized their potential, conducted research to assess adaptation of the principals, and developed the invention that is presented herein.
The first geophysical principal is based on work by Conrad and Marcel Schlumberger (1930) who developed a system of measuring the resistivity of surface rocks with electrodes deployed on the surface. The electrode spacing was typically 10""s of 100""s of feet and the objective of the investigation was to assess rock formation contact zones or geological structures, such as faulting and folding in deep subsurface zones. They used the subsurface zone variations in resistivity to interpret gross geologic structural phenomena. They later applied this technology to evaluating well bores drilled for petroleum exploration.
The second geophysical principal uses G. E. Archie""s 1941 work. Archie presented his work in 1942 in a paper entitled The Electrical Resistivity Log as an Aid in Determining Some Reservoir Characteristics. Archie determined porosities of various materials using resistivity measurements. Mathematical formulas that G. E. Archie derived, and other relevant mathematical formulas that have been adapted for use in the invention, are outlined in the DESCRIPTION OF THE PREFERRED EMBODIMENTS.
By combining these two petroleum exploration and production industries principles with modified geotechnical engineering equations for relative density, a new, accurate method has been developed for determining the geoelectric constants of a standard sample of porous materials as geo-electric tested ASTM 698.
Earlier researchers never provided a process or method for developing lab data that relates electrical resistivity to soil density because their focus was directed toward physical soil characteristics, not requiring electrical data for geotechnical engineering measurements and calculations. U.S. Pat. No. 5,861,751 combines the art of electrical geophysics with geotechnical engineering. Prior geophysical art includes the Wenner Electrode Array, which applies the Schlumberger theory by utilizing four electrodes that are spaced on the surface of the earth at equal distances. The distance between each electrode is commonly referred to as the xe2x80x9caxe2x80x9d spacing. In general, the depth of investigation is directly related to the electrode separation. J. J. Jakosky, (1950), discusses the depth of investigation, and notes that the theoretical depth of investigation should be equal to the xe2x80x9caxe2x80x9d spacing in a Wenner Array for a homogeneous medium.
In other electrode arrays, the depth of investigation can be as low as 20% of the length of the current electrode spacing from one end of the array to the other. The objective of applying the Wenner Electrode Array was to assess gross geologic features in the subsurface. The surface spacing for this purpose is 10""s of 100""s of feet, and the analysis yields an understanding of geologic structures in the subsurface. The key element in a typical investigation using the Wenner Electrode Array is the variation in the resistivity numbers. A single raw number alone would not allow interpretation of geologic structural phenomena, and is considered useless when out of context. A single resistivity number would not enable the assessment of geologic structural changes in the subsurface.
Anderson and Ehni chose a relatively small distance for the electrode separation in the Wenner Array installed in a nonconductive standard density mold. The objective of Anderson and Ehni""s work is to establish a set of geo-electric constants that are unique to a standard sample of material (SSM). These geo-electric constants that were established for the SSM are then used to calculate the in-situ density of the geotechnically similar porous material under test (PMUT). Using unprecedented short electrode separation installed in a standard density mold, Anderson and Ehni were able to measure a unique set of geo-electric properties of soil products.
In-situ density calculations using electrical geophysics were developed by Anderson and Ehni in 1996 and covered under U.S. Pat. No. 5,861,751. They use resistivity measurements and porosity calculations as developed by G. E. Archie, combined with a formation factor or constant. These formation and/or solution factors are empirically derived through experimentation and testing for repeatability.
The following professional papers were considered in the development of the present inventions:
Archie, G. E., The Electrical Resistivity Log as an Aid in Determining Some Reservoir Characteristics, Transaction of the American Institute of Mining and Metallurgical Engineers, Vol. 146, 1942
Cernica, John N. Geotechnical Engineering: Soil Mechanics, John Wiley and Sons, Inc., 1995
Hunt, Roy E., Geotechnical Engineering Investigation Manual, McGraw-Hill Book Company, 1984
McCarthy, David F., Essentials of Soil Mechanics and Foundations, Second Edition, Basic Geotechnics, Reston Publishing Company, Inc., 1982
Parasnis, D. S., Principles of Applied Geophysics, Fourth Edition, Published by Chapman and Hall, Ltd., New York, N.Y., 1986
Schlumberger C., and Scblumberger M.; Depth of investigation attainable by potential methods of electrical exploration . . . ; AIME Technical Publication No. 315; 1930
Schlumberger C., Scilumberger M., Leonardon E. D.; Electrical Coriing: a Method of Determining Bottom-hole data by Electrical Measurements.; Transactions of the AIME; Technical Publication No. 462; 1932
Vingoe, P., Electrical Resistivity Surveying, ABEM Geophysics and Electronics, Geophysical Memorandum 5/72; 1972
Wyllie, M. R. J. and Rose, Walter D., Some theoretical Considerations Related to the Quantitative Evaluation of the Physical characteristics of Reservoir Rock from Electrical Log Data, Gulf Research and Development Co., AIME Petroleum Branch, 1949
In U.S. Pat. No. 5,861,751, Dennis Anderson, P. E. and Bill Ehni have developed an efficient tool for measuring the in-situ density of porous materials. The present invention measures the geophysical properties of a standard sample material (SSM) using the testing apparatus and procedures, i.e. ASTM D1557 or ASTM D698, made of non-electrically conductive material and having a set, or sets, of electrodes installed for making geo-electrical measurements during the standard procedure. The resistivity measurements in conjunction with the moisture and density data are then used in the equations to empirically derive the geo-electric constants that are used in U.S. Pat. No. 5,861,751.
Front-end geotechnical analysis is an industry standard practice for construction projects that use earthen materials. The invention uses a general geophysical density equation (Anderson and Ehni 1996) that requires a set of empirically derived constants, The empirically derived constants that are used in the calculations for determining the in-situ density of the earthen construction materials are established for each soil type product that is scheduled for use in the construction. For each homogenous porous material a set of constants are established for use in the general geophysical-in-situ density equation.
The empirically derived constants are established by conducting pre-construction geotechnical tests. A series of lab tests using ASTM D698 or ASTM D1557 procedures are performed to establish an acceptable confidence level for repeatability for actual construction use with a given porous material that is considered geotechnically homogeneous. Once the constants are established, only two general geophysical-in-situ density equation variables, R and S, are field measured at each test site during the construction phase of the project. The following discussion compares the existing technology with the invention.
The present invention, when used in conjunction with U.S. Pat. No. 5,861,751 techniques, enables fast, efficient, and accurate testing of in-situ density of porous mediums. The field measurements can be performed during the foundation construction phase of building projects.
The new testing technology is the first application to employ electrodes in a standard proctor mold for deriving geoelectric constants. The invention""s primary advantage over existing technology is that it enables the fast field use of U.S. Pat. No. 5,861,751 which does not use a nuclear source, but still offer a high level of efficiency for QC/QA work and testing related to soil in-situ density
The invention has significant advantages over conventional QC/QA and environmental technology. The invention measures soil geo-electric density with electrical geophysical
Reference Numerals in the Drawings are as follows:
1. Current Electrode
2. Current Electrode
3. Potential Electrode
4. Potential Electrode
5. Non-electrically Conductive Primary Cylinder Cell
6. Non-electrically Conductive Primary Cylinder Cell Fixing Arm
7. Wing Nut
8. Non-electrically Conductive Top Sleeve
9. The notch cut-out in the top of the Non-electrically Conductive Primary Cylinder Cell and the bottom of the Non-electrically Conductive Top Sleeve so that the Top Sleeve fits over the Primary Cylinder Cell
10. Non-electrically Conductive Top Sleeve Fixing Arm
11. Wing Nut
12. Non-electrically Conductive Base Part
13. Bolt Non-electrically Conductive Base Part Non-electrically Conductive Base Part
14. Notch cutout in the top of the Base Part where the Non-electrically Conductive Primary Cylinder Cell is seated when the Base Part and the Primary Cylinder Cell are fastened together.
15. Notch cutout in the bottom of the Base Part such that the Wenner Array Electrodes in the Base Part are accessible for electronic wiring.